Field of the Invention
The present invention relates to a wireless communication, and more particularly, to a method and apparatus for decoding downlink control information in a wireless communication system in which the serving cells using radio frames of different types are aggregated.
Related Art
Long Term Evolution (LTE) based on 3rd Generation Partnership Project (3GPP) Technical Specification (TS) Release 8 is the leading next-generation mobile communication standard.
As disclosed in 3GPP TS 36.211 V8.7.0 (2009-05) “Evolved Universal Terrestrial Radio Access (E-UTRA); Physical Channels and Modulation (Release 8)”, in LTE, a physical channel can be divided into a Physical Downlink Shared Channel (PDSCH) and a Physical Downlink Control Channel (PDCCH), that is, downlink channels, and a Physical Uplink Shared Channel (PUSCH) and a Physical Uplink Control Channel (PUSCH), that is, uplink channels.
A PUCCH is an uplink control channel used to send uplink control information, such as a Hybrid Automatic Repeat reQuest (HARQ), an acknowledgement/not-acknowledgement (ACK/NACK) signal, a Channel Quality Indicator (CQI), and a Scheduling Request (SR).
Meanwhile, 3GPP LTE-advanced (LTE-A) that is an evolution of 3GPP LTE has been progressed. One of techniques introduced in 3GPP LTE-A is the carrier aggregation.
The carrier aggregation uses a plurality of component carriers. The component carrier is defined by a center frequency and a bandwidth. One downlink component carrier or a pair of an uplink component carrier and a downlink component carrier corresponds to a cell. It can be said that a user equipment provided with services using a plurality of downlink component carriers is serviced by a plurality of serving cells. The carrier aggregation includes a cross carrier scheduling of which a scheduling cell and a scheduled cell are different from each other and a non-cross carrier scheduling of which a scheduling cell and a scheduled cell are the same.
Meanwhile, in the wireless communication system of the next generation, the serving cells using different radio frame structures such as a serving cell using a time division duplex (TDD) radio frame and a serving cell using a frequency division duplex (FDD) radio frame may be aggregated. That is, a plurality of serving cells that uses radio frames of different types may be allocated to a user equipment. Or, although a plurality of serving cells that uses radio frames of the same type is allocated, an uplink-downlink configuration of each serving cell may be different.
Meanwhile, a format of downlink control information is predetermined. That is, which fields are included in the downlink control information is predetermined. In addition, a bit number of each field is also predetermined. However, there is a field of which bit number changes depending on whether a format of the downlink control is used in the TDD or the FDD.
In case that the cross carrier scheduling is applied in the wireless communication system in which serving cells using radio frame structures different from each other are aggregated, there is a problem that a size of the downlink control information format transmitted from a scheduling cell may be changed depending on whether the scheduled cell is a FDD cell or a TDD cell. In this case, there is problem that a blind decoding count of a user equipment increases.